Store-in cache users store data in the cache structure on the coupling facility. The data can be changed data (different from the data on permanent storage) or unchanged (the same as data on permanent storage). What distinguishes the store-in method from other cache methods is that store-in cache users write changed data to the cache structure but do not at the same time write the data to permanent storage (called hardening the data). This means that at any time, the data in the cache structure might contain changes not yet stored (or hardened) in permanent storage. Store-in users must periodically read the changed data from the cache structure and write, or “cast-out” the changed data to permanent storage.