The x36 and SDS lines of scanners are different than previous Uniden scanners. The "older" scanners have the programming (frequencies, etc.) written directly to the scanner. So all the data is in the scanner all the time. The "Clear Memory" routine is for someone who may have a corrupt memory or may otherwise want to "clean the slate".
The "newer" scanners have the programming data stored on the SD cards. That's because there is much more data for scanners. Statewide systems tend to be huge - more than older models can handle. So Uniden had to come up with a different way.
Based on the scanner user's preferences, some of the data is loaded from the SD card to the scanner memory when the scanner is booted up.
Thus, there isn't any "memory" to clear in the scanner itself. To "wipe the slate clean", one would want to format the SD card, then do a "Clear User Data". That erases saved frequencies and recordings.