Y would be.

Here is the video I mentioned before as I just found it again:


Basically he is doing something like this and I am unsure how M600 compares ->
Code:
M83 ; turn on relative movement for extruder  
G1 E-5.000000 F6000 ; retract filament 5mm  
G1 X0.000000 Y0.000000 Z4.000000 F9000 ; home X and Y axis leave Z at current height  
M84 E ; release extruder stepper motor from 'holding' position  
@pause ; pause print!
G1 X0.000000 Y0.000000 F9000 ; upon resume, rehome X/Y in case position was bumped out  
G1 X69.080000 Y58.560000 F9000 ; move back to next layer starting position  
G1 E0 F6000 ; reset extruder, ready to push out plastic again  
G1 F9000  
M82 ; set extruder movement back to absolute ready for next layer