I gleaned this from Bruce Wilcox's discussion of RiscIgo. He describes his move structure as:
What caught my eye is Kill Directions. How can 4 bits be enough information to replace captured stones upon undo? Ah, well of course! You just flood fill starting at the adjacent empty point(s).
is:
To undo this move, just flood fill with opposite color from the North (n) and South (s) points and then empty the location.
Nifty!