One work stream, separate chains
Dogecoin uses Scrypt proof of work. Through auxiliary proof of work introduced in 2014, compatible miners can submit evidence derived from the same mining work to Dogecoin while mining Litecoin or another compatible parent chain. Dogecoin still has its own block history, difficulty, rewards and node validation rules.
Merged mining does not merge DOGE and LTC balances or make a Litecoin transaction valid on Dogecoin. It lets miners reuse eligible work. A Dogecoin full node still decides whether a Dogecoin block follows Dogecoin consensus rules, and ordinary users do not need Litecoin to send DOGE.