Sitemaps question answered by the one who knows the best the Official Google Webmaster Central Blog.

Great post Posted by Mickey Kataria, Google Zürich

“Since the launch of Sitemaps, webmasters have been asking if they could submit their Sitemaps for multiple hosts on a single dedicated host. A fair question — and now you can!

Why would someone want to do this? Let’s say that you own www.example.com and mysite.google.com and you have Sitemaps for both hosts, e.g. sitemap-example.xml and sitemap-mysite.xml. Until today, you would have to store each Sitemap on its respective host. If you tried to place sitemap-mysite.xml on www.example.com, you would get an error because, for security reasons, a Sitemap on www.example.com can only contains URLs from www.example.com. So how do we solve this? Well, if you can “prove” that you own or control both of these hosts, then either one can host a Sitemap containing URLs for the other. Just follow the normal verification process in Google Webmaster Tools and any verified site in your account will be able to host Sitemaps for any other verified site in the same account.”

Read this post here!