As pure as the driven snow? What does that mean?

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Apparently, "as pure as the driven snow", or some such phrases, were used in Shakespeare's plays, and were supposed to mean the person was pure, untouched, unblemished. It was meant that the snow was "driven" by the wind, and didn't touch the ground as it fell. Now, see, I always understood it as an ironic phrase, understanding "driven snow" to mean that it is snow that sleighs/sleds have been driven through. Therefore, making the phrase mean that the person isn't as pure as they seem to be. What do you think it means?