debian - DHCP-Server - tell clients to renew lease

I have just set up a new DHCP server (dhcpd - package is dhcp3-server) on a Debian 6 box.
The new server is up and running, and I have successfully connected a client.

Formerly a router acted as the DHCP server.

My question: is there any way to send a broadcast to the network prompting all current lease holders - which still hold a lease from the router - to get a new lease from the new server?