Clarification about how messages are gossipped

[webglider]

Just a small clarification regarding how messages are gossipped. Is it like peers in a given channel gossip messages to each other and not to peers who are not in that channel? If that is the case then if there are no online peers in that particular channel a new peer which comes online wont be able to see any of that channel's chat history (even if there are lots of other peers online but none of them are in the channel of interest)? Or is it like messages are gossipped even to peers who are not in the channel?