Multiple Site Manager Homepages and Fields
What you're actually looking for here are the translation settings. These are stored against each field: in a multi-site installation, each field can be "translated" per site, per language or per site-group. ("Translated" is perhaps a confusing label here if your two sites are technically in the same language).



Set your Introduction field to be translatable for each site and it will be able to store unique content for each site.

This approach gives us lots of flexibility to have some fields with shared content and others with unique content, which cuts down the amount of duplicate editorial effort considerably on large multi-site installations where, for example, each site may want to use the same banner image but have different captions etc.