If you use Google webmasters tool to have pages in a sitemap from other domains, you can do that. A single Sitemap can contain pages from multiple domains as long as you have verified ownership of all sites.
Do you know that a single Sitemap can contain pages from multiple domains?
About Mohammad Shoeb
Hi, I'm Shoeb. I've been fortunate to work with WordPress for over a decade and I'm continuously learning from this journey. Alongside some wonderful people, I help run Elicus in Jaipur. Our aim is to make WordPress tools that are simple and helpful.