If you have Scrum on a larger scale in place, you will end up with several cross functional (multi-skilled) teams:
Eg. you will have developers, business analysts, and QA resources in one Scrum team. After a while you’ll need to think about know-how sharing and skill enhancements. I propose to implement communities of practice (CoP, http://en.wikipedia.org/wiki/Community_of_practice) for each skill.
A representative for each skill (horizontal community) is sent to the Scrum of Scrum.