There will always be a small amount of cache, like a few kb or a few mb, even after you clear it. You don't need to worry about that.

Hi ,

i already followed the instruction about wiping all cache. after that, i checked my installed apps, there are still cache. it means, it has no effect in my mobile.

Clear App Cache / Data:

NOTE: If one of your applications causes issues, takes up too much storage inexplicably, or just doesn’t work as intended, you might be able to fix these issues by clearing the app’s cache / data.

WARNING! Clearing an app’s data will also remove all of your personal data stored within the app, including high scores, saved games, profiles, login and credit card information etc. As such, you can avoid losing data by clearing only the app’s cache.

1. Tap “Apps” on the home screen
2. Open “Settings”
3. Under “Application”, tap “Application manager”
4. Go to “Downloaded” or “All”
5. Select the desired app and tap “Clear cache”
6. Assuming that clearing the cache didn’t solve the issues, you can tap “Clear data” > “OK”

Wipe the Cache Partition:

NOTE: In case your phone freezes, crashes, or is running out of storage inexplicably, you can try fixing these problems by clearing the phone’s cache partition.

1. First turn off the phone
2. Press and hold “Power”, “Volume Up” and “Home” at the same time
3. At the “Samsung” logo, release the “Power” key
4. When the “Android” logo appears, release all the hardware keys
5. Once you gain access to the “Android system recovery” menu, press “Volume down” repeatedly to highlight “Wipe cache partition”
6. Press “Power” to select the highlighted option
7. After the cache partition is cleared, “Reboot system now” should be highlighted
8. Press “Power” to restart your phone

NOTE: If clearing the cache partition didn’t help, you can visit this thread for instructions on how you can factory reset the Samsung Galaxy A9 instead.

Reboot in Safe Mode:

NOTE: If one of your third party applications causes issues and prevents you from removing it, you should be able to easily uninstall the app by first rebooting your phone in Safe Mode. In this mode all third party apps are disabled.

1. Turn off the phone
2. Press and hold “Power”
3. At the “Samsung” logo, release “Power” and immediately press and hold “Volume down” instead
4. After the phone finishes rebooting, release all hardware keys (NOTE: a “Safe Mode” label should be displayed in the lower area of the screen)
5. To remove an app, first go to “Settings”
6. Tap “Applications” under “Device”
7. Tap “Application manager”
8. Swipe to “Downloaded” and select the desired application
9. Tap “Uninstall”
10. Once the app has been uninstalled, press & hold “Power” to reboot your phone normally and exit Safe Mode