How to network multiple Arduinos so they react to the same signal
Rule 1 do not connect Arduino pins to long wires. 

You can achieve your your goal in many ways, a serial interface looks good from here.  I am doing it with a RS485 interface, note it is an interface not a protocol. You can use CAN, Wi-fi and many others.  It sounds like all the units except 1 will be receiving data, the other is transmitting it to the other devices.  RS485 will work good and it needs only 5V.  It will work over several thousand feet and some reasonable speeds. You can use a UART either hardware or software to accomplish the task with a RS-485 driver at each node.  You need to remember you need to wire from point to point with the terminating resistors only on the end nodes.