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). Two (2) forms of proof of address must accompany your application.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. Gov or submit in-person at the NYC Comptroller's Office. Typically, in order to claim US domicile, the Affidavit of Support sponsor must be residing in the United States. Domicile is a technical legal term.