Hi Sharath,
One time you configured the memcached node adding the instance in "Installed cache stores" (Dashboard - Site administration - Plugins - Caching - Configuration ) go to the bottom of page to the section "Stores used when no mapping is present" and "edit mappings" then in Cache administration select memcached as cache for the application. (I think this way you assign the memcached to all the possible options, I think).
Hope it helps!
Eduard.