RIM defines it as the following -
"the process of rewriting over memory to remove any residual unmapped data on the BlackBerry device. The scrubbing process could take up to several hours."
I am still trying to find out the exact details of scrubbing, as it is still a bit hazy, would love to post the exact method/mathematical formula/algorithm used.
I like this part -
"Note: Once scrubbing has been triggered, there is no way of stopping it. The process must be fully completed before the BlackBerry device may be used. Removing and reinserting the battery of the BlackBerry device will only start the scrubbing process again from the beginning.
The duration of the scrubbing process depends on factors such as the actual processor speed of the BlackBerry device, the amount of memory that it has, and the actual memory speed."