The Collaborative International Dictionary of English v.0.48:

Expunction \Ex*punc"tion\, n. [L. expunctio execution,
   performance, from expungere. See Expunge.]
   The act of expunging or erasing; the condition of being
   expunged. --Milton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

expunction
    n 1: deletion by an act of expunging or erasing [syn:
         expunction, expunging, erasure]