The number of homes lingering on the market fell 21% from year ago inventory levels, according to Pro Teck Valuation Services' May HomeValueForecast.

Pro Teck, a real estate valuation firm out of Waltham, Mass., said many cities pummeled by the foreclosure-crisis are seeing signs of stabilization due to increased home sales and reduced inventory levels.

"One of the most important developments in the past year for the residential real estate market has been the significant decline in the inventory of homes for sale," said Tom O'Grady, president and CEO of Pro Teck Valuation Services.

"Nationally, the number of homes currently listed are down 21% from a year ago."

A strong market generally has remaining inventory of five months or less, Pro Teck said. Right now, the U.S. market is dealing with a national inventory level of 6.3 months, the lowest level in six years.

The Rust Belt states of Michigan and Illinois are running contrary to their reputations as foreclosure-riddled states with metros in those states seeing significant declines in active real estate listings, according to Michael Sklarz, principal of collateral analytics for

On the other hand, many of the markets with higher inventory levels appear to be concentrated in the Northeast.

Some of the areas with double-digit percentages for inventory levels include Winston-Salem, N.C. (15.75 months of inventory); Virginia Beach-Norfolk-NewPort News, Va. (10.05 months), New York-White Plains-Wayne, NY (20.61 months of inventory), as well as the Midwest metro of Duluth, Minn. (38.70 months of inventory).