WordNet (r) 3.0 (2006):

clean slate
    n 1: an opportunity to start over without prejudice [syn: fresh
         start, clean slate, tabula rasa]

Moby Thesaurus II by Grady Ward, 1.0:

59 Moby Thesaurus words for "clean slate":
   blamelessness, blank, bloodless revolution, bouleversement,
   breakdown, breakup, cataclysm, catastrophe, clean sweep,
   cleanliness, cleanness, clear conscience, computer revolution,
   convulsion, counterrevolution, debacle, empty space, faultlessness,
   guiltlessness, immaculacy, impeccability, inanity, innocence,
   innocency, innocentness, nothing, nothing to hide, nothingness,
   offenselessness, overthrow, overturn, palace revolution,
   prelapsarian state, purity, radical change, reproachlessness,
   revolt, revolution, revolutionary war, revulsion, sinlessness,
   spasm, spotlessness, stainlessness, striking alteration,
   subversion, sweeping change, tabula rasa, taintlessness,
   technological revolution, total change, transilience,
   unblemishedness, unguiltiness, upset, vacuum, violent change, void,
   whiteness