How to check for Library swap between similar species

[apratap]

We have some libraries which we multiplexed for plant and on a
separate experiment for soil metagenome. We have a doubt that during
library preparation one or more of the libraries were swapped or even
a chance that two different index were put on the same library. Is
there a way to find which libraries were doubly indexed or swapped ?

Thanks!
-Abhi