When do things get cleared from Texture Memory?

I've been looking through the docs to try to find this out, but haven't had any luck. I'm trying to figure out when images get cleared from the texture memory in a channel-- are images that are no longer visible on the screen (after changing screens, for example) still in texture memory?

For example, if I open my channel, images on my channel's home screen are all loaded into texture memory. If I go to a different screen in my channel, are the previous images cleared from texture memory, and the ones on the new screen are loaded in?

Any insight would be much appreciated!