I use CCleaner from Piriform
to flush the notification tray cache. Works like a charm! Be advised that after you flush the cache, you'll need to restart Windows Explorer. This is easy though. Just start Task Manager (control+alt+delete) and end the explorer.exe process. Then select "file" from the Task Manager's menu and type in explorer.exe and hit enter. No more old tray icons!
Be advised before using CCleaner to uncheck all the options you don't want it to do. In other words, if you just want the notification tray icons flushed, make sure in CCleaner, that is the only thing selected. Not a huge deal but stuff like thumbnails can be flushed as well.