Hello - I have iCloud Messages turned on for all of my devices. When I deleted all of my messages on my iPhone, my messages on my Mac did not delete. It looked like some may have. Any help appreciated. Thanks.
They may not be able to delete historical messages that existed prior to iMessage synch. There may not be a universal identifier that let's the software know that message x on device a is the same as message x on device b. Just a guess...