You can clear the cached contents of a memcached server by giving it a "flush_all" command. You can do this with netcat (nc) or telnet.
echo "flush_all" | nc cache01.example.centoshowtos.org 11211
You can also telnet to the server, and issue a "flush_all" followed by "quit". It looks like this.
[user@host ~]$ telnet cache01.example.centoshowtos.org 11211(Comments)
Connected to localhost.
Escape character is '^]'.
Connection closed by foreign host.