Found on
https://www.osnews.com/story/9338/programming-the-cache-on-the-powerpc/

"On another point, there is no single proper cache flush instruction in the PowerPCs, an equivalent of the x86’s WBINVD ( Write Back and Invalidate ) so the only way to flush it is to fill it with dummy data."

"Why would you fill the caches with dummy data to flush? Never heard of DCBF, DCBI? Surely you have to go trough a loop for flushing, but no need to fill with dummy data. (BTW I feel it lot more sensible approach than the full cache flush at once.)"

I think you will have to find out the range of virtual addresses to flush and use the dcbf for each cache block.