If you want to sponsor someone for a family-based green card, you need to provide proof of a U.S. domicile in your Affidavit of Support (Form I-864). This guide will clarify what domicile is, how to establish it, and the documentation you need for proof of domicile.This guide will explain how to prove domicile when filling out Form I-864 ("Affidavit of Support"). Consular processing support without the high price tag. Typically, in order to claim US domicile, the Affidavit of Support sponsor must be residing in the United States. Gov or submit in-person at the NYC Comptroller's Office. Do I need to file a New York State tax return? How do I know if I am a resident of New York State for income tax purposes?