vlans in different subnet –issue of multicasting-pls help urgent

I have 2 vlans conncetd to L3 extereme switch.Both vlns are in different subnets.They send unicast packets in between But multicasting not working in between 2 vlans which are in different subnets.But multicasdting works in same subnet
.What to do to make up multicasting in between 2 subnets.