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It sounds like you have been able to get as far as putting the phone into download mode. Putting the phone and download mode by itself won't necessarily do anything but it does allow you to flash the operating system to the phone if that's what you need. You didn't really outline what your actual problem was – only what you have tried so I am making some assumptions. I also don't know to which instructions you are referring since I have no way of knowing what instructions you look debt. In any case,, I can probably help we just may need to clarify things before finally correcting it. If you're only trying to reset the device, and if you can get back to the screen where you cleared the cache, then you can go to that screen (this is called recovery) and instead of selecting the option to clear the cash, you can choose the option to do a factory wipe/reset.
You can use Samsung KIES, which is software available at their website. You can also do it using software called ODIN, but that is quite a bit more involved.
Are you running a MAC OS or Windows? If you are running Windows, then it should be fine.