The invention efficiently determines whether a container that is associated with an item of changeable data actually is associated with the freshest version of this item of changeable data. Multiple containers may exist in the virtual memory ("in-memory container") or in a persistent storage system ("persistent container") of a computer system and be associated with different versions of an item of changeable data. A table in the virtual memory reveals the freshness of changeable data associated with in-memory containers. One or more in-memory containers associated with one or more same items of changeable data are merged into a new persistent container and removed from the virtual memory. A persistent container is associated with a list that identifies all changeable data associated with the persistent container. An invalidation process invalidates, in the lists associated with older persistent containers, older versions of the changeable data associated with the new persistent container.