Would it be possible down the line to add a button when you Right click home/spaces or click Edit in the global menu to "Mark all as read" 

Why?
When you have been a way for a while or even over night they stack up the counter and its just nice to start fresh from the morning. Especially when you have a lot of (rooms)? 
When mobility is difficult as well going over to each room to clear them is a task that takes a long bit of time, Even difficult navigating to each when you use a non standard way of interacting the desktop.  
Since the other option is to open each room scroll up a bit then scroll down to clear them. Which depending on how far back you scroll you hit the scroll bug and not be able to scroll down.