When creating search scopes, consider the following:
If a search scope is created for a site collection, the scope will ONLY be available for the site collection where it was created. To create a shared search scope that will be available across all site collections, use Central Administration to create a shared search scope.
Site Actions -> Site Settings -> Site Collection Administration -> Search scopes
Application Management -> Manage service applications -> "Your Search Service Application" -> Queries and Results -> Scopes
After the scope is created, don't forget to display it. Modify "Display Groups" under site collection search scope settings.