This is a screen capture of a section of PWB where a 600-pin BGA is utilized.  You can see where the power plane is split (by the wide, bright red line).  The CAD software supports assigning different colors to different nets, as seen in the screen capture; pads that are green are connected to ground, bright blue are connected to the BGA Vcc, sky blue are connected to the "normal" Vcc, etc.