Unable to find the cache key in memcache

Question

I am using gem rabl for building my api response (https://github.com/nesquena/rabl).

In my controller, I have given like this

@cache_key = "rabl/spree/api/home/v2/index-en"

and in my index.rabl file, I gave,

cache @cache_key, expires_in: 15.minutes

I am using memcache for caching using the client Dalli and have deployed the application in heroku. Everything is working as expected. But when I am trying

Rails.cache.fetch('rabl/spree/api/home/v2/index-en')

I am not able to see any value. Why is it like this ? Does rabl append any value to cache key ?