How do I determine if an IOException is thrown because of a sharing violation?

private void RobustMoveFile( System.IO.DirectoryInfo destinationDirectory, System.IO.FileInfo sourceFile, Boolean retryMove )
            	{
            		try
            		{
            			string DestinationFile = Path.Combine( destinationDirectory.FullName, sourceFile.Name );
            			if ( File.Exists( DestinationFile ) )
            				sourceFile.Replace( DestinationFile, DestinationFile + "Back", true );
            			else
            			{
            				sourceFile.CopyTo( DestinationFile, true );
            				sourceFile.Delete();
            			}
            		}
            		catch ( System.IO.IOException IOEx )
            		{
            			int HResult = System.Runtime.InteropServices.Marshal.GetHRForException( IOEx );
            			const int SharingViolation = 32;
            			if ( ( HResult & 0xFFFF ) == SharingViolation && retryMove )
            				RobustMoveFile( destinationDirectory, sourceFile, false );
            			throw;
            		}
            	}