When a validation fires and prevents the update, it blocks the whole record update, not just one field. This is standard SFDC behavior.
Rather than using validation rules, you should consider using field level rights in SFDC (will block the field for all records, though), use the Marketo "block field update feature" (will also block for all records) or using a backup field to set the field back to it's value as soon as it is updated.
Thanks for your reply.
The Block field update feature in Marketo, would stop / block the sync from other source(SFDC) to marketo.
Enabling block field would not block sync form Marketo to SFDC, is what i foresee and understand. So our requirement is to stop sync for certain fields from Marketo to SFDC.
Besides this, may i ask if there is any statement as such "the validation error of one field, could stop sync of all other fields" in salesforce success community or anywhere as such. Please help and thank you for all your time.
Again, the validation error of one field in SFDC blocks the update of the whole record. This is standard SFDC behavior.
If you want to block field updates from Marketo to SFDC, it means that you want to block all source for a field update, excepted SFDC. You can indeed use the "Block Field Update" for this. The issue is that you cannot to this only for the synced records and leave the field free for the others.
See and vote Conditionally block field update with block / unblock flow steps . This idea would enable to select some records and block updates of fields for these records only.