So the only way I could resolve the issue and reset my tablet was to install CWM recovery (the last working link I found). I believe stock recovery would work as well, but I didn't have or find one.
The second step is to go the Settings → Backup & Reset → Factory data reset and clicking "Reset tablet". It will warn you about unavailability to backup or recover your data since device is encrypted and then will reboot device to recovery and provide factory reset.
Again, it would probably not be a problem if I'd have stock recovery. But in my case this was the only way to provide reset for my device and it took some time to find this out.
I also could try using restoring stock ROM with Kies or Odin, but I didn't have a working copy of Windows...
BTW here a few different ways you could try for other devices:
- If you know your password or you have a stock recovery it should not be a problem at all - just use the default way to wipe your data (through recovery or android settings).
- Use
fastboot erase userdata (it didn't work for me, because Samsung has no fastboot mode, they have their "Download mode", which is a bit different)
- Probably there is a way to reset/recover your device through some vendor provided tools (like Kies/Odin for Samsung devices).
- You are so unlucky :(. Try to search about how to do factory reset for your particular device.