The eligibility of domicile regarding the PCS exam is that the candidate needs to be a indian citizen. So if you are a citizen of India then you are eligible for the examination.

In PSC there can be some domicile conservation for the peoples of Bihar. So you may have some restriction in some of the PSC posts. But else most of them are opened for any citizen of India.

To know more about BPCS visit the link below:

https://www.google.com/amp/s/competition.careers360.com/articles/bpsc/amp

I hope my answer helps. All the very best for your future endeavors!