Recent Global Posts duplicating posts

In our installation we have some class blogs which syndicate posts from student blogs. What I am seeing is that Recent Global Posts is picking up the original post and the syndicated post. Is there a way to prevent Recent Global Posts from displaying the syndicated version of the post? A filter I can add to a simple plugin to prevent the posts on a Syndicated blog from being indexed by Post Indexer? Or can Post Indexer be made smarter so that it catches such duplicates?