When you go to the users tab on a mini-site, the reputation shown is their filtered reputation for that mini-sites filtered tags. Here is an example. But the rest of the site shows the users full reputation. Why the inconsistency? Why not show the users filtered reputation on questions, answers, profile pages, etc?
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Users are the same between Stack Overflow and Facebook Stack Overflow, this is by design.
So, when looking at a user or one of their posts you see their total reputation. If Marc B (the highest ranked PHP answerer of the last month) were to answer a facebook php question, his total reputation on Stack Oveflow is relevant (even though he hasn't been very active in Facebook tags).