From Django documentation for cache
Finally, if you want to delete all the keys in the cache, use
cache.clear(). Be careful with this; clear() will remove everything
from the cache, not just the keys set by your application.
You can also flush content of memcached by connecting by telnet or nc and executing flush_all
echo 'flush_all' | nc localhost 11211
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solved Cache._cache.flush_all () not working, How can I clear the cache with django and memcached?