To clear the DNS Forwarder cache, restart the dnsmasq daemon as follows:
Restarting the daemon will clear the internal cache, but the client PCs may still have cached entries. The DNS cache on a Windows PC may be cleaned from a command prompt or Start > Run:
This may need to be executed from an Administrator command prompt on Windows Vista and later.
Other operating systems will surely have other means to clear the DNS resolver cache. For example, Ubuntu-based distributions also use dnsmasq, and it may be restarted using:
sudo service network-manager restart
Browsers also have their own internal DNS caches separate from the OS. Close and re-open the browser if none of the above help.
As a last resort, rebooting/restarting a client will surely clear any locally cached data.