DNS Issues

I need some help in understand this one.. A disgruntled employee set up duplicate DNS for our domain on his personal server and convinced uu.net to update their DNS records to point to his server as our secondary DNS server. The record on his server has a different serial number than ours does, and we've contacted uu.net to point the domain back where it belonged. The question is how do I get the records to propagate rapidly?? he set the expire time on the records he sent out extremely high. Is there a way to force an update?? And what do the serial numbers really do? Thanks.