The operation needs to be blocking otherwise you could of course do it without CPU at all (DMA). But you still have to go through the memory controller and actually write each word of memory.
In fact all ones is not hard either, there were some experiments to give RAM ability to perform simple page-level computations with promising results.
I also wonder, for typical workloads, what percent of CPU time is spent zeroing pages.
The amount of time wasted zeroing out memory pages in a typical OS is quite significant, also take into account that such an operation will trash perfectly good cache space for no good reason.
In the end memory design is limited by the laws of physics.