Line allocation in multi-level hierarchical data stores

A storage apparatus for storing data is disclosed. The storage apparatus comprises: a plurality of stores having storage locations for storing data items, including a level one store and a level two store the storage apparatus having a hierarchy such that in response to an access request for accessing a data item the level one store is accessed and in response to detecting that the item is not stored in the level one store the level two store is accessed. The storage apparatus is configured to store a copy of at least some items in both of the one level one store and the level two store, the storage apparatus comprising a plurality of indicator storage elements associated with a corresponding plurality of storage locations of the level two store, a set value of an indicator stored in one of the indicator storage elements indicating that the corresponding stored data item is also stored in the level one store. The storage apparatus is configured such that in response to a request to allocate a storage location in the level two store, storage locations having a set indicator associated with them are not selected for eviction.