Home prices nationwide declined a slight 0.8% in August from July, according to the FNC Inc. residential price index. The decline may suggest housing activity is headed into negative territory after a brief seasonal rebound, the mortgage technology firm suggested. The slight decline reverses a four-month trend of price increases. FNC evaluates home prices for its index by analyzing both real-time appraisal data and public property records. The index excludes foreclosure sales. National home prices on a year-over-year basis are 4% to 5% lower than levels attained in August 2010, FNC said. The report broke home prices down by market and found that several cities, including Boston, Minneapolis, Phoenix, Portland, Los Angeles, San Diego, San Francisco, Tampa and Washington, D.C., felt the pangs of 1% to 3% price declines in August. When looking at price appreciation on a year-to-date basis, Boston, Dallas, Detroit, Houston, Minneapolis and San Francisco all showed price appreciation after rebounding during the selling season. Markets with significant price depreciation over last year include Las Vegas, Miami and Orlando — all of which experienced declines of 10% to 14.2%. Write to Kerri Panchuk.