Fire a RemoteEvent for all servers?

The somewhat recently-added MessagingService would be useful for this:

https://developer.roblox.com/en-us/api-reference/class/MessagingService

A server Script would listen to events like this:

local messaging_service = game:GetService("MessagingService")
messaging_service:SubscribeAsync("nuke_all_servers", function(extra_data)
	print("Received nuke event!")
end)

Another server script could "fire" the nuke event like so (obviously not a useful example):

local messaging_service = game:GetService("MessagingService")
local extra_data = "yada yada"

messaging_service:PublishAsync("nuke_all_servers", extra_data)