All variable names in Pd are global. There is only one name space for all patches.

The way to hack around this is to use $0 in variable names. For example, $0-foo.

$0 expands to a unique number for each abstraction - but not for each subpatch!

If you need to share a variable name between two abstractions, but no others, you could pass a "group identifier" into each of those abstractions and then use $n in variable names where n is the argument number of the group identifier. For example, "$1-foo". Variable names with $n in them work well with send and receive, but it is difficult (if not impossible) to get them into qlists.

This solution is discussed in the documentation.