There are two types of scrambling here - one is the bitswapping and byteswapping that you use to make DDR3/4 routing possible. The other is the whitening function for high speed data that ensures you don't have long sequences of the same value without a transition. The latter is a simple pseudorandom scrambler with a fixed random seed generated at boot. It is not cryptographically secure. The former is a simple substitution and quite easy to reverse (and trivial if you have either a schematic or a board to reverse). Both are deterministic and extremely vulnerable to known plaintext attacks. This is not a security feature.

Source: I'm working on a DDR4 layout right now, and the memory controller scrambling and swapping functions are documented in publically-available intel datasheets (for example, see https://www.intel.com/content/dam/www/public/us/en/documents... sections 2.1.6 and 2.1.8)