Could someone tell me how to force a zone transfer?

I have BIND running on my OES Linux server, with two slave zones, and I'm
trying to force a zone transfer with the master on a NW 6.5 server. There
are changes on the master, the serial numbers for the zones have been
incremented, and the master is configured to notify all secondaries. As I
understand it, the notification should cause the secondaries to compare
serial numbers and update their zones if the serial number on the master
is larger that the serial number it has in its zone. But no updates are
taking place.

Is there some way to force the zone transfer? Is there something I'm

Thank you.