I believe there is a proper order when flushing the system to minimize contaminating new fluid with old fluid. Normally it is recommended to start with the furthest wheel from the master cylinder first and get closer and closer. But with ABS I think it is different. For a WRX it is RF, LR, RR, RF or something like that. I imagine the Legacy is has a similar brake system.
I need to find out what the proper order is for the Legacy