A domicile of origin is given to every individual at birth by operation of law, which can be changed by acquiring a domicile of choice by the combination of 1) residence and 2) intention of permanent or indefinite residence.

However, in probate cases, when the court has to determine which law applies to the deceased’s estate, a lot of time it is difficult to establish the deceased’s intention to reside in a country permanently because the deceased can no longer testify such an intention.  In the circumstances, such intention shall be inferred from surrounding circumstances, such as the location of death, the location of the majority of the estate, the length of stay of one country, social habits, employment etc.
In the event that the deceased’s domicile is not in Hong Kong, permission must be granted by the Probate Registry in order to proceed with the application pursuant to rule 29 Non Contentious Probate Rules.  In the event that no grant has been issued by the country which the deceased was domiciled, the law of the countries which the deceased was domiciled is often required to be submitted, by way of affidavit made by a competent lawyer, in order to establish that the applicant is entitled to the grant under the laws of that country.  This process can be time consuming and costly.

Moreover, if inheritance tax is levied on the deceased’s estate at the country which the deceased was domiciled, the estate in Hong Kong may be subject to such inheritance tax, notwithstanding that the assets is not situated in that country.

Case Study:-
Robert, a British expat born and raised in the UK, relocated to Hong Kong due to work with his wife and two young children for seven years, and he enjoyed his life in Hong Kong very much that he moved most of his assets to Hong Kong, bought an apartment and intended to live in Hong Kong permanently.  He was applying for permanent residency in Hong Kong.
Robert left a real property in the UK which he inherited from his parents, and it is rent out during his time in Hong Kong.  Apart from that, the majority of his assets are in Hong Kong.
Robert passed away in an accident without leaving a will. 

Immediate upon his death, his bank accounts in Hong Kong are frozen, which cannot be dealt with until a grant of probate is issued by the Hong Kong court.  Grant of probate is also required when his wife wishes to inherit his real property in the UK.
Because of Robert’s UK domicile of origin, his assets is subject to worldwide inheritance tax, which is 40% at present above the threshold of £325,000.00, unless his wife can successfully convince the UK government that Robert acquired Hong Kong as his domicile of choice, which would be deduced from Robert’s living pattern hence difficult.
Moreover, when his wife applies for grant of letters of administration in Hong Kong, because of Robert’s intestacy, she needs to produce an affidavit signed by an UK solicitor confirming that she is entitled to the grant of letters of administration under the UK laws, notwithstanding that Hong Kong laws on probate follows UK laws.
Result: his family can only inherit his assets after paying substantial inheritance tax, and going through a complicated and costly application for letters of administration in both UK and Hong Kong.

If only Robert made a will declaring Hong Kong as his domicile, the probate application can be substantially simplified, and his wife can potentially save substantial amount of tax because of his Hong Kong domicile hence his Hong Kong estate is not taxable.

Conclusion
Domicile can be a tricky concept which can be difficult to understand but cannot be ignored.  Consult your lawyer in order to protect your wealth against potentially substantial tax liability.