Clear chat on server entrance

When a player comes from another server to my server, I dont want them to see the chat of their previous server because they dont pay attention to the welcome message.

Is there any way to clear the old chat on the client with a server command?

 

I don't know if they go though but I guess you could try sending a bunch of empty lines to the player. Won't clear the chat but it will push it up far enough it won't be visible unless he scrolls.