Domicile is key here - an individual's domicile is a legal issue - you can't become temporarily domiciled somewhere. Domicile in simple terms is where the individaul has his permanent home. E.g. and individual born say in the US, who has their family, investments, pension etc there, and comes to Ireland for a few years for an undetermined length of stay, but with the intention to return to the US, retains a US domicile while resident in Ireland.
(P.S. this is a very broad generalisation of domicile - you would need to get specialist advice to confirm an individual's domicile). PM me if you want more details.
An individual who is not domiciled in Ireland (but residnet) is taxable on gains arising outside the state (with the exception of the UK) only to the extent that the gains are remitted to Ireland.
Hope this makes sense.