1. A data processing apparatus, said data processing apparatus comprising: data processing circuitry configured to perform data processing operations on data; a hierarchical cache structure configured to store at least a subset of said data for access by the data processing circuitry, said hierarchical cache structure having a first level cache and a second level cache, the hierarchical cache structure being responsive to an access request issued by the data processing circuitry and specifying an address, to access in the first level cache the data identified by the address if that data is stored in the first level cache, and to seek to access in the second level cache the data identified by the address if that data is not stored in the first level cache, and any data evicted from the first level cache being routed to the second level cache; access control circuitry associated with the second level cache and configured, in response to data evicted from the first level cache, to perform an eviction handling operation requiring access to the second level cache; cache maintenance circuitry configured to perform a cache maintenance operation requiring cache maintenance to be performed in both the first level cache and the second level cache; if the cache maintenance required in respect of the first level cache during performance of the cache maintenance operation causes data to be evicted from the first level cache, the cache maintenance circuitry being configured to cause maintenance indication data to be passed to the second level cache in association with the evicted data; the access control circuitry being responsive to the maintenance indication data to modify the eviction handling operation performed in response to the evicted data in order to cause the required cache maintenance for the second level cache to be incorporated within the eviction handling operation.