By default the 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 Memcache to store cached data in the object cache persistently across page loads to speed up your site.
You can clear this cache by using the Flush Object Cache button in your Site Settings in the MyPressable Control Panel. If your site is experiencing a lot of traffic, this can cause site speed issues as the entire cache is purged.
If you need to regularly modify specific data in the 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.