How would you manage scope creep while using the Agile approach?

The only reason I have seen in my experience so far for scope creep is inability to evaluate a requirement completely. This results in surprises which must be managed on top of current backlog thus increasing tasks list. 

Agile Approach take us in a thought process of first deciding the final outcome of any project and then creating approach with quantum of milestones.

Scope creep occurs because of unclear final outcome, this problem can be solved by initially setting the final outcome and then working for projects with quantum of milestones. Backtrack and Backlogs keeps a project in deterministic state. And let the deliverables be quantifiable which in turn resolves the scope creep issue of Project Management which occurs in traditional approaches.