Hi VB,
Assuming you are talking about F2e/F3 series line cards, the forwarding engine is the Switch on Chip (SoC). Each SoC services a set amount of ports on the line card - for example, the 48-port 1/10GE fiber line cards use one SoC per four physical ports.
The MAC table, FIB/adjacency table and ingress/egress buffers are integrated within each SoC to service the ports connected to it.
This approach explains some of the scale variance when using the Nexus 7k platform, for example if you contain layer 2 domains to SoC's you can scale the MAC tables significantly higher than layer 2 domains spread across SoC's where replication is then required between them.
This is also the reason why there are restrictions around allocating groups of ports to a VDC - you cannot allocate ports from the same SoC to multiple VDCs.
For useful links, you can watch the Cisco Nexus 7000 Switch Architecture presentation from Cisco Live 2014 - the session name is BRKARC-3470 (https://www.ciscolive.com/online/connect/sessionDetail.ww?SESSION_ID=77694). This provides really great insight as to how the internals of this platform function.
