By default WordPress object cache is non-persistent. This means that data stored in the object cache resides in memory only and only for the duration of the request. However, Pressable uses Memcached to store cached items in the object cache persistently across page loads to speed up your site. Queries must be cached very deliberately, making use of Core WordPress functions in the WP Object Cache class.
You can clear this cache by using the Purge Cache button in your Site Setting Control Panel. This will also clear all page and static asset caching. If your site is experiencing a lot of traffic this can cause site speed issues as all of the cache’s are replenished.
If you need to regularly delete, replace, or clear any of your object cache it is advisable to use the built in WordPress functions for this:
Determining which function to use comes down to what you are trying to achieve.