User filters are designed for the use case you describe.Here's some links to our online help and Knowledge base about this topic:
If you haven't done so yet, please check out the following article: http://kb.tableausoftware.com/articles/knowledgebase/row-level-security-and-user-filters.. It talks about setting up region specific users with Tableau Server.
Hope this helps,
Looks like Andy C was a bit quicker on the submit button this morning -