the CLEAR cmd already does that
Code:
   CHK?RP  FSR0L
   movlw   low (RAM_END)
   movwf   FSR0L
   movlw   high (RAM_END)
   movwf   (FSR0L) + 1
loop    clrf    POSTDEC0
   movf    FSR0L, W
   iorwf   FSR0H, W
   bnz     loop
   clrf    INDF0
you are still left with the dilemma on how to fill all the "ram" your pbp code has claimed to a value other than 0
so you can detect the end of pbp's allocation, might as well examine the .lst
have found pedja's pgm is not correct when include files are used {as warned}

you could always do it like most c compilers
they just keep allocating ram from the heap until the stack underflows ,then let the pgm crash and burn