Sorry, all, for some reason I didn't get a notification about more posts on this thread until this morning! I will edit the original post to make it clear that foreign works don't need to worry about this because foreign works are protected by the Berne Convention for the Protection of Literary and Artistic Works. I think even if a non-US citizen wanted to sue in US court for copyright infringement, you would not first have to register with the US Copyright Office because US courts will look to the Berne Convention and apply that in lieu of US copyright law.