To flush redis cache without restarting the service, follow this guide

First find out what port + IP address redis is running on:

netstat -plnt | grep redis

Output will look similar to:

tcp        0      0 10.x.x.26:6379          0.0.0.0:*                   LISTEN      5972/redis-server 1 

You will first need to get the password from the local.xml file in the document root.
The format is normally path/to/document/root/app/etc/local.xml

grep -i password path/to/document/root/app/etc/local.xml

Ouput will look like:

                    <password><![asjpAJSPAkspaks]]></password>
                <password>aNSLAjsAJMS;MAs;sA</password> 

Password you normally need is the second one. If you less the file instead you can check for the CDATA[memcache] section.
Now we need to telnet using the information from the netstat grep

telnet 10.x.x.26 6379

Run the command INFO to see if you are authenticated:

INFO

-NOAUTH Authentication required.

Now authenticate with the password:

AUTH reallylongpassword

Confirmation you have authenticated:

+OK

Now we need to flush the cache:

FLUSHALL

RUN INFO