When this feature is enabled, the Cortex-A9 processor can write entire non-coherent cache lines full of zero to the L2C-310 cache controller with a single request. This provides a performance improvement and some power savings. This feature can optimize the performance of the processor, but it requires a slave that is optimized for this special access. The requests are marked as write full line of zeros by having the associated AWUSERM0 bit set.
Setting bit  of the ACTLR enables this feature. See Auxiliary Control Register.
You must program the L2C-310 Cache Controller first, prior to enabling the feature in the Cortex-A9 processor, to support this feature. See the CoreLink Level 2 Cache Controller (L2C-310) Technical Reference Manual.