The Collaborative International Dictionary of English v.0.48:

Scour \Scour\ (skour), v. t. [imp. & p. p. Scoured; p. pr. &
   vb. n. Scouring.] [Akin to LG. sch["u]ren, D. schuren,
   schueren, G. scheuern, Dan. skure; Sw. skura; all possibly
   fr. LL. escurare, fr. L. ex + curare to take care. Cf.
   Cure.]
   1. To rub hard with something rough, as sand or Bristol
      brick, especially for the purpose of cleaning; to clean by
      friction; to make clean or bright; to cleanse from grease,
      dirt, etc., as articles of dress.
      [1913 Webster]

   2. To purge; as, to scour a horse.
      [1913 Webster]

   3. To remove by rubbing or cleansing; to sweep along or off;
      to carry away or remove, as by a current of water; --
      often with off or away.
      [1913 Webster]

            [I will] stain my favors in a bloody mask,
            Which, washed away, shall scour my shame with it.
                                                  --Shak.
      [1913 Webster]

   4. [Perhaps a different word; cf. OF. escorre, escourre, It.
      scorrere, both fr. L. excurrere to run forth. Cf.
      Excursion.] To pass swiftly over; to brush along; to
      traverse or search thoroughly; as, to scour the coast.
      [1913 Webster]

            Not so when swift Camilla scours the plain. --Pope.
      [1913 Webster]

   5. To cleanse or clear, as by a current of water; to flush.

            If my neighbor ought to scour a ditch. --Blackstone.
      [Webster 1913 Suppl.]

   Scouring barrel, a tumbling barrel. See under Tumbling.


   Scouring cinder (Metal.), a basic slag, which attacks the
      lining of a shaft furnace. --Raymond.

   Scouring rush. (Bot.) See Dutch rush, under Dutch.

   Scouring stock (Woolen Manuf.), a kind of fulling mill.
      [1913 Webster]

WordNet (r) 3.0 (2006):

scouring
    n 1: moving over territory to search for something; "scouring
         the entire area revealed nothing"
    2: the act of cleaning a surface by rubbing it with a brush and
       soap and water [syn: scrub, scrubbing, scouring]

Moby Thesaurus II by Grady Ward, 1.0:

140 Moby Thesaurus words for "scouring":
   ablation, ablution, abrasion, abrasive, afterglow, afterimage,
   attrition, balance, bones, buffing, burnishing, butt, butt end,
   candle ends, chafe, chaff, chafing, cleaning out, culm, deadwood,
   debris, detrition, detritus, dishwater, douche, douching, draff,
   dregs, dressing, dust, elution, elutriation, end, enema, erasure,
   erosion, fag end, filing, filings, flush, flushing, flushing out,
   fossil, fretting, galling, garbage, gash, grazing, grinding,
   hogwash, holdover, husks, irrigation, lathering, lavabo, lavage,
   lavation, laving, leavings, lees, leftovers, limation, mopping,
   mopping up, odds and ends, offal, offscourings, orts, parings,
   polishing, potsherds, rags, rasping, raspings, refuse, relics,
   remainder, remains, remnant, residue, residuum, rest, rinse,
   rinsing, roach, rubbing away, rubbish, ruins, rump, sandblasting,
   sanding, sawdust, scourings, scrap iron, scrape, scraping, scraps,
   scratch, scratching, scrub, scrubbing, scrubbing up, scuff, scum,
   shadow, shampoo, shards, shavings, shining, slack, slag, slop,
   slops, smoothing, soaping, sponge, sponging, straw, stubble, stump,
   survival, swabbing, sweepings, swill, tares, trace, vestige, wash,
   washing, washing up, washout, washup, wastage, waste, waste matter,
   wastepaper, wear, wearing away, weeds, wiping up