You want to flush your DNS cache in linux? Well it is very very easy :]

Let's say you use systemd-resolve:

easy!

$ systemd-resolve --flush-caches

Let's say you use anything else (nscd, dnsmasq, named etc)

easier!

just restart the service

$ systemctl restart nscd (or dnsmasq, named etc)

or if you do not use systemd, you could try

service nscd restart

cheers!

PS: you probably need to have root privileges to execute the above commands