That depends on where you call it from. You don't seem to be setting any kind of a flag there that indicates that you've already sent the destroy call.
Also you are sending this notification to everyone... not sure why. You're checking TNManager.isHosting inside -- so only one player can effectively receive it and execute the code inside. Wouldn't it be easier to get rid of that function altogether, and just do both TNManager.Create and TNManager.Destroy calls where you're calling the RFC? It's also inside if (TNManager.isHosting) after all...
And don't forget to set some "destroyed" flag, or this code will execute again on the next update (assuming that's where you put it).