What if my search engine covers multiple domains that I own?

Since on-demand indexing currently accepts only one Sitemap at a time, if you'd like to specify pages from multiple domains for on-demand indexing, you'll need to create a single Sitemap that includes URLs for multiple websites. A single Sitemap can contain pages from multiple domains as long as you have verified ownership of all sites. For more details about creating cross-site Sitemaps, visit the Webmaster Help Center.