There is an interesting device in the OpenComputers mod that allows you to determine the block hardness at a distance.
But the trouble is, the data it gives out is rather noisy and the greater the distance, the more noise.
To determine the true hardness of a block, we can scan it several times and average the result. The noise that interferes with scanning is of a probabilistic nature. And after several scans, you can statistically find what the most likely hardness of the block is.
In one tick, we can scan 64 blocks. To analyze the entire available area (65 x 65 x 64) with hundred of