Another interpretation:
McCrea in gaelic: "Son of Grace"
Chery in french: "Dear, Darling", aka "mon cherie"
So McCreachery could have meant something along the lines of "Dear Son of Grace". Which would make sense since he was a devout Christian.
http://www.thinkbabynames.com/meaning/0/Chery
http://www.thinkbabynames.com/meaning/1/Mccrea
I think we have a winner!