If your other microcontrollers are far away from master, then RS485 is good choice.
About your basic question RS485 is meant for multipoint communication,
When you transmit data on RS485 bus, every controller listen, i.e. every controller receives the data. Now its upto ur algorithm and device adressing, which will decide if u want to process data or not.
For sample programm, you just write in slave controller common address like 0x00,
means if incoming data is for 0x00 device it will receive and process the data, it is called broadcasting.