You can create a TOC for each document part by first applying a bookmark to each section. Then, in the field code for the local TOC, you would add a switch and the bookmark name.
Default TOC field code:
{ TOC \o "1-3" \h \z \u }
After editing to include section bookmark:
{ TOC \o "1-3" \h \z \u \b SectionBookmarkName }
Please post again if you need help implementing this.