Ok, here is very nice post about Reachability: http://www.mikeash.com/pyblog/friday-qa-2013-06-14-reachability.html (check comments below!)
Tldr: You can fire block when your connection is back, but this solution is not perfect. There is no 100% reliable way to do this (except trying in loop), but you can try to mix those approaches.
Edit: Comment to @Jonah.at.GoDaddy answer:
Reachability can give you both connection notification errors: false positive and false negative (you can check it at WWDC 2011 session, I don’t remember which one; there are two about networking). So, my point is: you should never rely only on those notification. You can trigger refresh on status change, but there should be another way of doing it (user interaction, or some kind of active waiting).