baz.com doesn't take control over foo.com, and it's not invisible. You click on a link and the domain changes, it's as old as the internet itself. The only difference is that the new page will be embedded into the old one, instead of there being a clear cut transition.
(and you can be sure that anyone that dosen't allow google to "portal" their pages will be damnatio memoriae'd into oblivion on results pages)