To clear a cache simply turn box off for about 30 seconds and then turn back on.

Those clear cache buttons have not nor will they ever clear a cache. They simply clear your recents and that's all they do pure and simple. In fact they should be named "clear recents". A quick switch of users will partially clear the cache negating having to power off then power back on but to totally clear the cache read the opening sentence above.

Turn your box off and wait say 5 to 10 seconds before turning back on and see how long it takes for the first light to come on. What is really occurring is the main server is performing "I am off routines" or muttering "can't this person make up their mind", LOL.

Turn your box off wait say 30 seconds before turning back on and see how quick the first light comes on. Now the cache has been cleared after performing the necessary routines.

You told the main server I am off and thus your priority of service is last. The server is performing routines and among them is clearing buffers aka your cache. After an "all seems well", ASW, signal you go back to being a priority but not as high as those already on line which is numero uno. Now when the routines are done and you turn your box back on another ASW signal is sent looking for a wink back and bingo the light comes on PDQ.

Another timing of clearing your cache method is to send yourself a message and when the red message waiting, MW, light is lit turn the box off and quickly turn back on. When you turn off you'll notice the MW light naturally goes out. When the MW light is lit then the cache is clear.