There are two values in play here, and the way your question is phrased makes me think you're confusing them.
Every block has:
- A hash (computed by double-SHA256 the block header, including timestamp, nonce, version, Merkle root, nBits which encodes the difficulty, and previous block hash)
- A target (computed from the difficulty only)
000000000000000000084bc771b929b0780276b1c31cec10a96921b1e53b970a is the hash of block number 669945. Just feeding the block's header exactly to double-SHA256 gives you this output (including the zeroes up front). It gets interpreted as a number:
- 0x000000000000000000084bc771b929b0780276b1c31cec10a96921b1e53b970a (in hex, with zeroes explicit)
- 0x84bc771b929b0780276b1c31cec10a96921b1e53b970a (in hex)
- 794600089940753232651370066465976921098309156434843402 (converted to decimal)
The target is the maximum allowed value that hash must have to satisfy the proof-of-work requirement. It is determined entirely by the difficulty(*) (which on its turn is determined by the timestamps of the previous blocks in the chain it is built on). That difficulty is also stored in the block header itself as the "nBits" value. The nBits value for block 669945 is 0x170d21b9; it encodes 0x0d21b9 · 2560x17 - 3, which equals:
- 0x0d21b900000000000000000000000000000000 (in hex)
- 1257769770588612382309009370720465882998915202417688576 (converted to decimal)
Since 794600089940753232651370066465976921098309156434843402 (the actual hash's value) is less than 1257769770588612382309009370720465882998915202417688576 (the target value), proof-of-work is valid for this block. And of course it is; if it wasn't, you would never have heard about this (attempted) block candidate.
(*) Technically speaking, the term "difficulty" is only used for representing how hard a block is for human consumption. Internally only nBits and the full target value are ever used. Difficulty is defined as 0xffff·25626 / target. The lower the target, the harder it is to find a block whose hash is below it, and thus the higher the difficulty is.