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 explain how to prove domicile when filling out Form I-864 ("Affidavit of Support").Consular processing support without the high price tag. In this post, we'll explore examples of proof of US domicile and the documents required to establish proof of domicile. What are the most important for the I864 are the proofs of US income or US employment or US assets. Typically, in order to claim US domicile, the Affidavit of Support sponsor must be residing in the United States.