Of course, rebooting the phone is simply turning it off, then back on again. A system cache clear shouldn't erase any of your data; here's how to do it:
Power down phone
Hold volume up/down & power simultaneously
Use volume down to navigate to 'Recovery', use volume up to select
Should see screen with triangle and exclamation point next to an Android
Press volume up/down simultaneously
Use volume rocker to navigate to 'wipe cache' and use power button to select
Once finished, use volume rocker to navigate to 'reboot system now' and use power button to select
