Hello Amar
The scope keyword in the command is used to specify the time to live (TTL) value in the IP header of the Auto-RP discovery messages. The value used here should be large enough to ensure that the discovery messages will reach all of the routers within your PIM domain. But it should be small enough to prevent the unnecessary relaying and retransmitting of the discovery messages.
More information about this command can be found here:
I hope this has been helpful!
Laz