Tax residence is determined under the domestic tax laws of each jurisdiction.

There might be situations where a person qualifies as a tax resident under the tax residence rules of more than one jurisdiction, and therefore is a tax resident in more than one jurisdiction. 

The mere right to reside in a given jurisdiction (on permanent or temporary basis) or the fact of holding citizenship of a given jurisdiction does not automatically mean that a person shall be considered a tax resident in such a jurisdiction or that, upon obtaining residency or citizenship, the tax residency is extinguished in the former jurisdiction(s) of tax residence.

At Hanover Bond Law we help clients who work and live across multiple jurisdictions, in particular the UK, Italy, Spain and Germany navigate the complex issues that surround tax residency. It is often the case that through small adjustments to someones lifestyle and habits or through preemptive disclosure to the local tax authorities, clarity can be achieved in a way so as to avoid issues with tax authorities in futures. 

If you are the employee of a company  and you get posted abroad, it is advisable that you seek your own independent advice on the tax implications of the move for you personally. It is often the case that companies get advice on this point by their own advisers.  Such advise is usually strongly caveated, which means that ultimately you cannot rely on it. As you point this out to your employer, they are usually willing to pay for the independent advice. So you get your peace of mind at no cost.