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). If you're planning to petition a family member for a green card, you'll most likely need to prepare Form I864, Affidavit of Support.This guide will clarify what domicile is, how to establish it, and the documentation you need for proof of domicile. Proof of U.S. domicile is required for the I864. Learn examples of proof of domicile along with proof of domicile documents required. 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. There are several requirements to submit an I864 Affidavit of Support. The proof of U.S. domicile is one of those required documents.