This is incorrect.

If sRGB (1,1,1) is XYZ (1,1,1), then sRGB (0,0,0) is XYZ (0.0025,0.0025,0.0025).

Or if you are using absolute XYZ values, sRGB (0,0,0) is XYZ (0.1901,0.2,0.2178).