ArchivesSpace keeps track of what has been indexed by using the files
under data/indexer_state. If these files are missing, the indexer
assumes that nothing has been indexed and reindexes everything.
To force ArchivesSpace to reindex all records, just delete the
directory /path/to/archivesspace/data/indexer_state. Since the
indexing process is cumulative, there's no harm in indexing the same
document multiple times.