Some folks do, although it's a little tricky to build all the right campaigns in Marketo to catch all the cases. There are also several partners on http://launchpoint.marketo.com/ which do data cleansing as well.
See my many instructions on how to do this. http://www.marketingrockstarguides.com/marketing-rockstars-guide-to-marketo/ http://developers.marketo.com/blog/how-to-clean-your-marketo-database/
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