19. The apparatus of claim 16 , wherein when returning the subcache in response to the filtering query, wherein the execution mechanism is configured to indicate a maximum size allowed for the subcache and indicate a maximum age and a purgeable age for identifiers for images in the subcache.
19. The apparatus of claim 16 , wherein when returning the subcache in response to the filtering query, wherein the execution mechanism is configured to indicate a maximum size allowed for the subcache and indicate a maximum age and a purgeable age for identifiers for images in the subcache. 20. The apparatus of claim 19 , wherein each subcache includes a maximum age and purgeable age limit, wherein the execution mechanism is configured to: remove an identifier for an image from the cache if the identifier for the image is older than the maximum age limit, wherein when removing the identifier for the image, the execution mechanism is configured to removing the underlying image from the location in memory or on disk; mark the identifier for the image as purgeable if the identifier for the image is older than the purgeable age; and wherein when an identifier for an image is marked as purgeable, the wherein the execution mechanism is configured to remove the associated image from the location in memory if wherein the execution mechanism requires the location in memory for another purpose.