Who should refactor someone else's code?

Question

Refactoring

Let's say there are 5 developers. One of them (let's call him Developer A) starts refactoring a class as part of his task. Others also used this class or its descendants in their tasks.
Developer A now has to fix the whole code (the volume can be quite large) or fix the current at home, and let the rest make updates themselves. How do you deal with this issue in your team?