The following code worked for me correctly:
~LButton::
MouseGetPos, x,y
if (x > 800 and x < 1500 and y < 600 and y > 200)
MouseMove, 1000, 400
return
where 800, 1500, 600 and 200 are boundaries of desired area. If clicked inside it, the cursor will be moved out to a position 1000, 400.