Is there a sharding? So each Master & Verification shard contains & processes only one piece of blockchain.
Yes and No.
Incoming transactions are collected by multiple nodes and then sent to verification nodes that prepare sub-blocks for masters, masters merge the sub-blocks together, forge the block and seed to torrent nodes.
It's a very simplified story.
Please check YP for a network diagram:
https://static.metahash.org/docs/MetaHash_YellowPaper_EN.pdf?v=6