DNS Client under linux
How-to Flush the DNS Cache on Linux
To flush DNS cache root access is required.
# sudo systemd-resolve --flush-caches resolvectl flush-caches
You can then check the statistics in order to make sure that your cache size is now zero, thus cleared.
# systemd-resolve --statistics resolvectl statistics
If systemd is not available on your system try
sudo service dns-clean restart
or (this should be exactly the same)
sudo /etc/init.d/dns-clean restart
How-to see DNS you use
# systemd-resolve --status resolvectl status