As I stated in my answer to What are the main differences between InnoDB and MyISAM?, MyISAM only cache indexes. There is only one setting for the global key cache. It is called key_buffer_size. MyISAM also features the use of dedicated key caches (I have many posts on this).
I see you are inquiring about MariaDB's Aria storage engine. There is a global key ...
As for now
We plan to also add CACHE INDEX for Aria tables if there is a need for this.
And as you can see that it is written in https://mariadb.com/kb/en/cache-index/ so that it would be more like the MyISAM, but as development and theory grows in time, we will see and wait, what they actually want to do qand implement.